Field of the Invention
The present invention relates to a technique for panoramically expanding an omnidirectional image.
Description of the Related Art
Omnidirectional images shot with an omnidirectional camera or the like and covering 360 degrees are known. An omnidirectional image is an image that is shot with an omnidirectional camera or a camera in which a fish eye lens is used and has, within a field angle, an entire range of 360 degrees in the horizontal direction. An omnidirectional image has a donut shape as shown in FIG. 1A, and therefore is an image hard to view for a viewer if displayed without any processing. In view of this, expanding the omnidirectional image in FIG. 1A into a panoramic image as in FIG. 1B through image processing (hereinafter, referred to as panoramic expansion) is commonly performed. The entire range (360 degrees) of the omnidirectional image having a donut shape is panoramically expanded such that the omnidirectional image is divided at an arbitrary position in the horizontal direction (circumferential direction of the omnidirectional image having a donut shape), image processing is performed so as to make the circumference of the omnidirectional image follow a straight line, and a panoramic image covering all the directions is generated. The divided position will be the two ends of the panoramic image.
As a technique for determining a divided position during this panoramic expansion, Japanese Patent Laid-Open No. 2006-191535 discloses a technique in which face recognition is performed on an image that was panoramically expanded at an arbitrary position, and in the case where a person overlaps with the divided position, a divided position is determined again and the panoramic expansion is started over.
However, Japanese Patent Laid-Open No. 2006-191535 envisions a usage mainly for performing shooting with a fixed camera such as shooting of a conference, and a case of reproducing a moving image made up of omnidirectional images shot while moving a camera (hereinafter, referred to as omnidirectional moving image) is not considered. In an omnidirectional moving image shot while moving a camera, the movement of a stationary object involves approaching the camera from a distant position (appearance point) in the image, and subsequently moving away to a disappearance point on the side opposite to the direction of movement. At this time, if the divided position for panoramic expansion is an inappropriate position, the movement of the object in the image appears to be unnatural, giving a feeling of strangeness to a viewer of the panoramically expanded moving image.